a new pcb etching soultion!

i found this on the make group in instuctables not only is it cheaper but its also reuseable.
i might do it(once i will be old enougth to buy the chemicals )
**broken link removed**

Sorry charlie. Not even close to new. People have doing it for ever. In fact, curpirc chloride is the standard industrial etchant for PCB production.

:O
sorry i didn't know it was old im seriously sorry you can delete this if you want

depends on your definition of new, or perhaps your point of view ... perhaps to the OP, the method was new, as in, newly known.

Hydrochloric acid by itself is the etchant in this case, the cupric chloride is a byproduct of the reaction and helps limit the rate of reaction.

Though I'm still basically using Ferric Chloride (which creates cupric chloride as a waste product during etching), the other commonly used ammonium persulfate is probably the most interesting non-full acid etchant as it's clear and will make the solution blue as it etches. It's not any less dangerous than any other chemical, however.

And in either case, the copper ions that you're flushing down the drain is the most environmentally unsavory item anyway (the iron is fine.)

boxer4 said:

ammonium persulfate is probably the most interesting non-full acid etchant as it's clear and will make the solution blue as it etches. It's not any less dangerous than any other chemical, however.

Click to expand...

How do you feel about Sodium Persulphate?

A couple of points

CuCl is, in fact, an etchant and it has the positive distinction of being renewable. It produces significantly less hazardous waste. There are numerous pages that describe this process. The chemistry is more complex than you would think.

However, it is tricky to get right as it requires some chemical expertise to keep it going. I've played with it a fair amount and could never get it to work that well with out adding HCl and/or H2O2. The first couple of etchings, are indeed HCl based.

APS is much less noxious than the other etchants. It has an NFPA 704 health rating of 2. FeCl has a 3. Higher is worse. In addition, it doesn't stain nearly as badly as FeCl.

FeCl dyed my hands yellow-brown for over 3 months...

Everybody would ask what happened.

Ferric Chloride: FeCl3(aq) + 3Cu(s) -> Fe(s) + 3CuCl(aq)
Yes, this stuff stains, but iron ions are less toxic than copper ions (Copper poisoning is more likely than Iron poisoning. There's a _lot_ more iron in a human body than copper. I suppose it's moot because we're creating copper ions during the etching process so we're making more toxins...)

I suppose Cupric Choride could do:

CuCl2(aq) + Cu(s) -> 2CuCl(aq)

forming cuprous chloride, but I suppose this redox reaction does not strongly favor CuCl without some sort of catalyst or secondary reaction. But with the acid in place it will favor 2Cu + 2HCl -> 2CuCl + H2 redox. I'm not a chemist though (also the 2HCl + 2CuCl -> 2CuCl2 + H2 will replenish the CuCl2 sacrificing the HCl. However this can't be self sustaining unless copper is removed from the solution - you're going to keep on getting more and more copper chlorides!

I suppose Sodium Persulfate is also pleasant to work as it's clear, but I suspect since it's a redox with sodium, this would cause bubbles to form which may not be a good thing:

2Cu(s) + Na2(SO4)2 + 2H2O -> 2CuSO4 + 2NaOH + H2(g)

Again I'm not a chemist so this might be totally wrong, but that's my guess at the reactions... (The ammonium persulfate would produce ammonia which dissolves fairly easily in water, so that's not nearly as bad)

I think the Instructable understates the danger. Mixing HCL with H2O2 makes a lot of heat. Will melt a plastic container and more to the point can spatter and blind you if done improperly.

It's not really "reusable", it's more like the solution craps out partway through and you can't finish it off without bubbling some air through it. The acid is still consumed and you can add more, but the new acid is being diluted in spent solution (just H2O). Just like when your FeCl3 is half used up, it's a mixed bag to speed it up again by adding some more FeCl3 because the added chemical is being diluted into the spent solution yielding lower concentration than the fresh FeCl3 had, and the whole problem you were trying to solve is a low concentration of active chemical.

But then again these reagents are delightfully cheap.
It sure would be nice to get a better concentration by using something other than 3% peroxide. You can get stronger but it's dangerous, high concentrations can actually set common stuff on fire.

I wonder if you could plate out the copper with electrolysis...?

Oznog said:

I wonder if you could plate out the copper with electrolysis...?

Click to expand...

This guy seems to have done it. The results look a bit rough mind.

**broken link removed**
The Saltwater etch process - Instructables

That's an interesting way to etch, however, the solution still becomes filled with copper chloride and thus not plated out. The more annoying part of it is this: it would be difficult to make sure all unwanted copper is constantly connected to the power supply (else it will just sit there for a while) and thus explains why it's so rough looking - because it is...

Eternally replenishable PCB etching solution (based on persulfate-type etchant)

I have got a way to recycle and reuse persulfate-type copper etchant infinitely. Its an electochemical setup that will cost you a lot when you set it up for the first time. But it does not require any kind of maintainence. You dont have to add any chemicals later. You can reuse the same solution forever.

THEORY : First, I will discuss the theoritical principles involved.

sodium/ammonium persulfate (Na2S2O8 / (NH3)2S2O8) etches copper in the following way :-

Na2S2O8(aq) + Cu(s) ----> Na2SO4(aq) + CuSO4(aq)

The electrochemical mechanism reverses this in the following way :-

CuSO4 ---> (Cu)2+ + (SO4)2-

At cathode (-ve electrode) :

(Cu)2+ + 2e ---> Cu (copper gets deposited on the electrode itself, thus removing copper ions from the solution)

At anode (+ve electrode) :

2 (SO4)2- ---> (S2O8)2- + 2e

Thus the persulfate ions ,ie. the primary oxidiser, is regenerated from the sulfate ions.

REQUIREMENTS : You will need the following components to set up your etching apparatus.

1) a platinum electrode (1 pcs) for the anode : This will be the most expensive component in the whole apparatus. Also note, there are two varieties of Pt electrodes. A) The platinized platium electrode , which is black or grey in colour because it is coated with Platinum Black (an allotrope of platinum), and, B) The shiny platinum electrode, without the coating, which has a shiny silver-like appearance. You are supposed to use the shiny-type Pt electrode. The black one won't work.
2) a copper electrode for the cathode : you may use a length of a copper wire (after striping off the insulation) or a spare bit of copperclad pcb. Make sure this electrode has a large surface area.
3) a glass/plastic container to hold the solution and act as your etching tray
4) sodium persulfate (Na2S2O8) : Alternatively, sodium sulfate (Na2SO4) may be used to begin with and sodium persulfate can be generated from that by electrolysis.
5) a little bit of conc. sulfuric acid (H2SO4) to lower the pH a bit : an acidified solution helps to speed up the etchant-regeneration process.
6) water : ordinary tap water would do but distilled water is better.
7) Power Supply - a mechanism to supply a lot of current (about 5-10 Amps) at controlled voltages to the electrodes : A simple 9-volt battery with a potentiometer might do. But a 9-volt battery can't supply sufficient amount of current. So the regeneration process may be too slow to be acceptable. A better way is to draw the power from the house-electric supply. Use a 12-volt DC wall transformer/adapter to get a 12V DC source of current. Then prepare a custom voltage-regulation circuit that uses the 12V DC output and can provide 5-10 Amps at a voltage that you can control precisely.
(Note : the required output voltages are typically between 0.5V to 4.5V DC with a control precision of atleast 0.1V)
8) You can also add an agitator mechanism (aquarium pump) and a heater mechanism (immersion heater / aquarium thermostat) to the apparatus to speed up the etching process.

SETUP THE APPARATUS :-

Prepare a sodium persulfate solution at a concentration of 230 gram/litre. If you are starting with sodium sulfate instead of sodium persulfate, mix at a concentration of 460 gram/litre. Add to it about 10 ml of conc. sulfuric acid per litre of the solution. Your etching solution is ready.

Now pour your etching solution in your etching tray and drop the electrodes in it. (the copper electrode is supposed to be the cathode (-ve) and the platinum electrode is to be anode(+ve). Make sure you connect them correctly.)

Now, if you mixed your solution with sodium persulfate, you are ready to go. But if you used sodium sulfate, you need to run a current through the solution so that sodium persulfate can be generated within the solution. Calibrate the voltage of the regulator and let the current run for some time (about one hour). (The voltage calibration process is being given below, as a part of the etching process.)

THE ETCHING PROCESS :-

Drop the pcb, which is to be etched, in the solution and start a current in the circuit.

Then you need to adjust the potentiometer or the v-reg to supply the correct voltage.
The goal would be to set the voltage as large as possible but just short of when a vigourous bubbling starts at the platinum anode.

(Note, if you are are using an aquarium air-pump to agitate the solution, you must turn it off during this voltage calibration process. Otherwise you wont be able to distinguish the bubbling at the anode. After calibration, you can turn on the pump and leave the apparatus to etch your pcb.)

Ideally, You must begin with a voltage as low as possible and increase the voltage until you can see a lot of bubbling at the anode. Once you find the threshold point, you must set the voltage to slightly less that.

POST-PROCESSING OF ETCHANT SOLUTION :-

After etching is completed, remove the pcb from the solution and let the current run for some more time. This will allow all copper ions dissolved in the solution to get deposited on the cathode and clean-up the solution. (It is easy to detect presence of copper ions in the solution. Copper ions impart a blue colour to the solution. So wait till the blue colour fades away)

After this process completes, you must remove both the electrodes from the solution before you remove power from the electrodes. If you remove power from the electrodes while they are in the solution, the cathode which is made of copper, turns into an ordinary copper rod, and the etchant immediately starts eating away copper from the electrode. So if you leave the cathode in the solution without power supply, the etchant will essentially get used up and you will need to regenerate it again before you can use it.
Note that, although the solution doesn't react with the platinum electrode, but if left in it for a long time, it can corrode the suface. And you don't want the most expensive part of your etching apparatus destroyed.

Best of Luck with your new etching system
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Addendums

**broken link removed**

That link explains the cupric chloride process including all the chemistry- and no- it does not use HCL as the etchant- it is also renewable with a minimum of fuss.

Hi,

I have used the salt water etching process years ago to etch identification
marks into tools. You dont really need that much salt in the water either.
The tool itself is one electrode, and you need another electrode maybe out
of a carbon rod or something.
The longer you leave it in the deeper the marks come out.

You can do boards like this too because the copper gets etched out the
same way. The trick is that ALL of the copper to be etched MUST be connected
to the electrode at all times, or else nothing happens. To get this to work,
all you have to do is make sure that all the traces are connected with at least
one thin line which can be later cut out with a sharp knife. This is an added
step of course and for complex boards it would mean cutting out lots of
short thin copper lines between traces before the board could actually be used.

It works great for tools because the metal between the lettering never becomes
separated from the body of the tool so it continuously etches until you turn
off the power.

DC power would be best, with a small experiment to determine best polarity.

as i know You could use 80g of crystals(amunium salphate)with 300mL of hot water. The crystals should fully dissolve to form your etchant solution which will appear clear and colourless. Since you should'll actually go with 40g of crystals and 150mL of hot water (note that the ratio should remain the same).
shani from pakistan

This is a hobby, if you are interested in DIY.